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Mosquitoes are some of the deadliest creatures on Earth. Now, scientists have taken a major step toward developing a “mosquito birth control” drug that can help prevent diseases responsible for several million human deaths annually around the world.

Researchers at the University of Arizona (UA) discovered a protein in mosquitoes that is critical to the insects’ process of producing viable eggs. When researchers selectively blocked the activity of the protein in female mosquitoes, the mosquitoes laid eggs with defective egg shells, leading to the death of the embryos inside.

In a report published in the open access journal PLoS Biology on Tuesday, the researchers said the protein — which they named Eggshell Organizing Factor 1, or EOF-1 — exists only in mosquitoes, so any drug developed to control mosquito populations would not affect other organisms, such as beneficial honey bees.

“We specifically looked for genes that were unique to mosquitoes and then tested for their functional role in eggshell synthesis,” said Jun Isoe, a research scientist in the lab of Roger Miesfeld, a UA Distinguished Professor and head of the Department of Chemistry and Biochemistry, and research team lead. “We think there are other discoveries to be made using this same species-directed approach.”

Mosquitoes are one of the deadliest animals in the world. Their ability to carry and spread diseases, such as Zika, dengue, chikungunya, and yellow fever, to humans causes millions of deaths every year, according to the World Health Organization (WHO). In 2015, malaria alone caused 438,000 deaths.

To find the EOF-1 protein, the research team first identified 40 genes unique to mosquitoes. Then they used a technique known as RNA interference, or RNAi, to inhibit these genes one by one.

The RNAi molecules were injected into female mosquitoes right before a blood meal. And out of the 40 mosquito-specific genes the team tested, only one, the EOF-1 gene, was found to disrupt eggshell formation and result in the death of the mosquito embryo.

The team also found that the effect of a single RNAi injection lasted for the lifetime of the mosquito.

Images obtained through electron microscopy revealed that when mosquitoes are deficient in the EOF-1 protein, the females lay eggs with abnormal-looking egg shells.

Eggs laid by mosquitoes treated with RNAi against the EOF-1 protein (right) and a control (left) display striking differences in the shells. (Photo Credit: Jun Isoe)

The team believes a strategy involving drugs designed to selectively interfere with mosquito EOF-1 can result in eggs that never hatch into larvae — and thus serving as a birth control for mosquitoes.

“Since the days of DDT, we have known that mosquito population control works to reduce the incidence of human disease,” said Miesfield. “This could be a next-generation tool that could be applied to bed nets and other areas frequented by mosquitoes.”

Miesfield’s team has filed a provisional patent on the species-specific discovery process as a first step into an application that could be commercialized.